Mass spectrometer



June 16, 1953 A. c. scHRoEDER 2,642,535

MASS SPECTROMETER Filed Oct. 18, 1946 4 Sheets-Sheet 1 Focus/N6 ,Po TEN r/AL AceaMAr//w Y Euer/voos v INVENTOR Alfred C J'croeder ATTO R N EY MASS SPECTROMETER Filed Oct. 18, 194 4 Sheets-Sheet 2 mi Z D/ F3 AME cmg/QR ma. K fl L @-93- 75 MMAL A502555@ W6 79 l@ '9' da g affair/wmv a? 5 Paw/5 f7- 43 25' .2 9 /jg i 231 HMH 06a. f @652m y L l IMM a? 7.9 F510. 55 @j @feas/mmv@ 77H5 17 29 bis 43 25 we am hi 25' INVENTQR Ww/# 5 a5 F. Amed C. Mmm/e @i E-ll. BY Kirai/M5 f'T//V ATTORN EY June 16, 1953 A. c. scHRoEDER 2,642,535

MASS SPECTROMETER 'n Filed oct. 18, 194e 4 sheets-sheet :5

041/7750 Fak F35 Dicen/mmf@ 0R PULSE l F35 91 @JZ l Llf' @.161

INVENTOR '3d/fied C .S'Craea/ef @QM ATTORNEY June 16, 1953 A. c. scHRoEDER 2,642,535

MASS SPECTROMETER Filed Oct.A 18, 1946 4 Sheets-Sheet 4 21 9 f2s 8 L 3 J/GA/HL DL/W15, Amr/Pam,

.93 l I life! l ATTORNEY Patented June 16, 1953 MASS SPECTROMETER Alfred C. Schroeder, Feasterville, Pa., assignor to Radio ACorporation of America, a corporation of Delaware Application October 18, 1946, Serial No. 704,116

Claims.

This invention relates generally to improved methods of and means for analyzing charged particle radiations and more particularly to improved mass spectrometers and the like for analyzing the relative abundance and masses of ions or other charged particles` Among the objects of the invention are to provide an improved method of and means for measuring the relative quantities and masses of charged particle radiations. Another object is to provide an improved mass spectrometer for analyzing gaseous specimens. `An additional object is to provide an improved mass spectrometer having a linear mass indicating scale.A A further object is to provide an improved mass spectrometer or the like wherein ions derived from a source to be analyzed are accelerated by extremely short duration, square wave accelerating potentials, the accelerated ions are segregated according to their relative velocities so that they reach a target velectrode at successive time intervals, and signals derived from the target electrode are applied to a cathode ray oscilloscope to provide indications of the relative abundance of particles of predetermined diferent mass.

Other objects of the invention are to provide an improved mass spectroscope utilizing square wave accelerating and/or decelerating voltage pulses for segregating ions of different mass. An

additional object is to provide an improv-ed mass u spectrometer utilizing accelerating and/or decelerating square Wave voltage pulses for segregating ions of diierent mass, and ion deflecting means for selecting or rejecting ions Withinpredetermined mass limits. A further object is to provide an improved mass spectrometer utilizing sc uare Wave, short duration, accelerating and/or dccelerating pulses for segregating ions of diierent masses, and ion multiplying signal plate means responsive to the accelerated and/or decelerated ions for providing signals characteristic of the relative abundance and mass of the ions to be analyzed.

A still further object of the invention is to provide an improved mass spectrometer or the like wherein ions to be analyzed are accelerated by short duration square wave pulses and projected against anion-sensitive mosaic; resultant potentials established upon the mosaic vbeing scanned by a cathode-ray beam to provide an output signal characteristic roi the relative abundance and atomic weight of the projected ions. Another object is to provide an improved mass spectrometer wherein ions to'be analyzed are accelerated by short duration, square wave pulses, and the (Cl. Z50-41.9)

2 accelerated ions are collected and indicated as a function of their'diferent travel times. A still further object is to provide an improved mass spectrometer providing constant indications of the relative abundance and atomic weight of ions derived from a source to be analyzed.

Briefly, the system required for Vproviding theA improved mass spectrometer comprises an envelope enclosing an ion source (ormeans for generating ions from gaseous samples introduced therein), an ion accelerating space, an ionseparating space, and a target electrode or screen.`

lin a special case the accelerating and separating spaces may be combined. The ions entering the accelerating space pass through Yan' apertured partition to the separation space, and travely to an ion-sensitive target electrode or mosaicy from which potentials lmay be derived characteristic' of the relative abundance and velocities, or travell times, of the ions impinging thereon. Ionized particles from the source are accelerated by successive square-wave, short-duration pulses of accelerating potential, and pass into the separating space Where the accelerated particles of dilferent mass are separated by any of a number of methcds which will be described hereinafter.

For example, in the simplest form of the invention, ions leaving the ion source are accelerated in the accelerating space by a pulse of such short duration that the ions to be observedA have not yet reached the end of the accelerating space. (Ions which are lighter than those to be examined or separated may already have entered the separating space, and in some forms of the Vinvention these particles are separately analyzed or excluded.) Because all of the particlesto b e analyzedV have been accelerated for the same length of time, the lighter particles will travel faster than the heavier ones at the conclusion of the acceleration pulse interval. If no further forces act upon the particles, the lightest ones Will traverse the separating space more quickly than the heavier ones, and the various particles Willstrke the target electrode or mosaic at Ytime intervalsl determined by their relative mass.

The time of flight of a particle from source to target will be directly proportional toits mass (if initial velocities are neglected). If the target electrode is coupled to a suitable oscilloscope or other indicating apparatus, ak series Aof pulses of different magnitudes, depending upon the quantity of ions which produce each indicator pulse, and spaced in time proportionately to the mass of the particles, will provide continuous indications of the relative abundance particular signal i lightest particle to and mass of the particles under observation. One of the coordinates of the oscilloscope may be calibrated in relative quantities of ions, and the other coordinate may be calibrated directly in atomic weight of the particles under observation. If a space occurs between adjacent pulses corresponding -to a particular atomic weight, the absence of ions of this particular atomic weight in the specimen is indicated. The calibration range of the instrument may be varied by changing the magnitude or duration, or both, of the accelerated pulses, or by changing the characteristios'of the timing signals applied to the oscilloscope. It should be understood that thev timing signals must be synchronized with, and properly phased with respect to the accelerating pulses.

If instead of utilizing extremely short accelerating pulses, they are of longer dur-ation, so that the particles of interest leave the accelerating space before the conclusion of the accelerating pulse, the time required for a particle to traverse the space to the target will be proportional to the square root of the mass of the particles. This type of operation crowds together the indications of the heavier particles, if examined in the same manner as described heretofore, and if the accelerating pulses are relatively long, some or all of the indicated pulses may overlap adjacent ones. By differentiating and/or rectifying the signals derived from the signal plate and applied to the oscilloscope, the indicated pulses may be separated from each other, but the atomic weight scale still will be proportional to the square Aroot of the relative masses of the particles.

If greater separation is desired between particular pulse indications on the oscilloscope, a decelerating pulse of proper duration and amplitude to slow down some or all of the particles (but not stop them) can be applied to the particles as they traverse the separating space, or in any event immediately before the lightest particle to be examined reaches the target. A decelerating pulse also may be applied to the particles in the accelerating space just before the be examined leaves the accelerating space. This type of operation produces a separation of the pulses arriving at the target equivalent to a very' much shorter accelerating pulse. However, the effect applies only to particles heavierthan a desired minimum value, which can be as small as l.

A further manner of providing greater segregation of the times of arrival of particles of different mass at the target electrode is to apply a decelerating bias in the accelerating space during the time that the accelerating pulse is not applied thereto. The decelerating bias slows down the heavy particles more than the lighter ones since the lighter ones pass into the unbiased separating space sooner than the heavier ones because they are closer to the separating space when the accelerating pulse is concluded. All particles heavier than some predetermined mass, determined by the sizev and duration of the acceleratingpulse, the amount of decelerating bias, and the length of the accelerating space, are decelerated to zero velocity, or less, and returned to the source.

When employed a decelerating field to maintain substantially all of the ionized particles in the region of the source except during the intervals of the accelerating pulses, it is possible to employ higher gas pressures in the ion source, providing the gas is substantially completely ionized. This operation also permits the use of an ion source of larger area wherein the ion forming electrodes may be shaped so that the ionized particles are focused to a point, preferably at a target. Such a focused ion beam permits greater signal output than an unfocused one. If desired, the signals derived from the signal plate may actuate .an ion multiplier (of similar characteristics to an electron multiplier), or the signal plate potentials may be amplified prior to application to the oscilloscope or other indicator.

If, in a mass spectrometer operated with a short duration accelerating pulse, a steady deflecting field is applied to part or all of the separating space, the particles of different mass may be caused to strike different parts of the target..

This feature has been employed in prior art devices to segregate ions of different atomic weight which have been accelerated by sawtooth accelerating potentials. In an improvement upon such known devices, and in accordance with the invention, the target may comprise a fluorescent electrode or screen so that particles of different mass may be seen directly upon dierent portionsY of the fluorescent target, the deflection thereof being characteristic of the relative masses of the various particle groups. Also if desired, the target electrode may be fluorescent, and at the same time a signal plate, in which case the quantity of ions would be determined by the measured magnitudes of the indicated pulses, and the mass by the relative position of the indicated pulses on the fluorescent screen. plate or iiuorescent target screen might be sufficiently small so that only particles of one predetermined mass could be observed at any one time, the deflection voltages applied to the separating space being adjusted to analyze separately groups of particles of each desired mass. Furthermore, magnetic or electrostatic fields may be applied to the separating space to vary the relative segregation of the particles of different mass.

Various other methods and means for provi-d- Y ing other combinations and arrangements of accelerating pulses, decelerating pulses and/or deflecting systems, as Well as various types of nuorescent screen or signal plate targets will be described hereinafter in greater detail by reference to the accompanying vdrawings wherein Figure l is aschematic diagram of a preferred embodiment of the system, Figure 2 is a graphic example of a typical cathode ray oscillographic indication provided by the circuit of Fig. l, Figure 3 is ak schematic ion ray diagram of the system of'Fig. 1, Figure 4 is a focusedl ray diagram for4 such a system, Figure 5 is a ray diagram indicating acceleration, deceleration and deflection of the ion beam in a modification of lsaid system,`

Figure 6 is a cross-sectional, partially schematic view of a second embodiment of the invention utilizing an ion mosaic and cathode ray scan'-` ning system, Figure 7 is a schematic diagram of a system utilizing an extremely short duration accelerating pulse in the accelerating space, Figure 8 is a'schematic diagram of the system show'- ing a relatively long accelerating pulse in the accelerating space, Figure 9 is a schematic diagramY of the system showing a relatively short accelerating pulse in the accelerating space and a relatively long decelerating pulse in the separating space, Figure 10 is a schematic diagram of the system showing successive accelerating and decelerating pulses "applied to the acceleratingl space, Figure 11 is a schematic diagram of the system showing a decelerating bias applied If desired, the signal to the accelerating space exceptl during the interval of Ia relatively short accelerating pulse, Figure 12 is'a schematic diagram of the system showing a relatively short accelerating pulse applied to the accelerating space and a much longer duration decelerating pulse applied to the separating space, Figure 13 is a schematic diagram of the system showing an ion multiplier forming a portion of the ion target of the system of Fig. 1, Figure 14 is a schematic diagram of the system showing steady electrostatic deflection of ions projected toward a fluorescent screen target electrode, Figure 15 is a schematic diagram of a system similar to that of Fig. 14 wherein the fluorescent screen also is a signal plate coupled to a cathode ray oscilloscope, Figure 16 is a schematic diagram comprising a modication of the systems of Figs. 14 and 15 including a movable target collector electrode, Figures 17 and 18 are schematic diagrams showing further modifications of the systems of Figs. 14, 15 and 16 and including both electrostatic and electromagnetic deiiection of the accelerated ions, Figures 19, 20 and 21 are schematic diagrams of the system including the deflection of the accelerated ions by means of short duration deflection pulses applied to the ions in the separating space. Similar reference characters are applied to similar elements throughout the drawings.

Referring to Figure 1 of the drawings, the system includes an evacuable envelope I having an input port 3 connected to a source of gas to be analyzed and an output port 5 connected to a vacuum pumping system. The ion generating source within the evacuable envelope includes a thermionic cathode 'I, a cathode shield 9- having an aperture II therein, and an anode I3 maintained at positive potential with respect to the cathode shield 9 by an anode battery I5. Atoms of the gas to be analyzed pass through the path of the electron beam between the cathode and anode electrodes, are ionized and the ions are accelerated by the eld produced by accelerating pulses applied to an adjacently disposed accelerating electrode Il. field in the accelerating space between the accelerating electrode I'I and the cathode shield 9 are projected through a central aperture I9 in the accelerating electrode and traverse a separating space 2| to impinge upon a signal plate target 23. As explained heretofore, the short duration, square-wave accelerating pulses establishing the field in the ion accelerating space (between the accelerating electrode I'I and the cathode shield 9) accelerate each of the gaseous ions` to a degree inversely proportional to the mass thereof, whereby the lighter ions reach the signal plate earlier than the heavier ones, and all ions of a particular mass reach the signal plate at substantially the same instant, thereby bunching the ions according to mass, and developing voltage pulses upon the target 23. The voltages developed upon the target 23 are .ampliiied by an amplier 25 and applied to the vertical deflection elements 21 of a cathode ray oscilloscope 29. Timing voltages for providing horizontal deiiection of the cathode ray oscilloscope 29 are derived from a timing generator 3| .and applied to the horizontal deiiecting elements 33 of the oscilloscope.

lThe accelerating pulses, comprising short duration, square wave negative pulses 35, are produced by an accelerating pulse generator 3l which is synchronized with the timing generator 3| through anadjustable phase control 39. n The The ions accelerated by the timing generator 3| may comprise, for example. a sawtooth, low frequency generator to provider a linear time scale for the oscilloscope, and the accelerating pulse generator 3'I may comprise a conventional keyed multivibrator which is actuated by synchronizing pulses 4I derived from the adjustable phase control 39 and the timing generator 3|. Either positive or negative polarity synchronizing pulses may be employed for initiating the accelerating pulses, depending upon the particular multivibrator circuit arrangement utilized for the accelerating pulse generator 31. Multivibrators for generating successive positive and negative pulses of the same or different duration in each complete cycle of operation are generally known in the art, and such devices may be keyed by synchronizing pulses to provide any desired typev of accelerating and/or decelerating or deiiecting pulses. If desired, the zero voltage level of the pulses may be varied by adding or subtracting D.C. potentials to the pulses.

The indications provided upon the fluorescent screen of the cathode ray oscilloscope 29 may be as shown in Fig. 2 wherein the vertical axis is characteristic of the quantity or abundance of ions, and the horizontal axis is a linear function oi ion mass or atomic weight. It is noted that in Figure 2 no indication is provided at the point corresponding to an atomic Weight of 19. This indicates that no ions of this particular atomic weight are present in the gas under analysis,

whereas the relative vertical deflections at other atomic weights indicate the relative abundance4 of ions having such atomic weights. The vertical f indicating scale may be adjusted by varying the sensitivity of the amplifier or lby adjusting the magnitude of the accelerating pulses applied tov l establish the accelerating iield. The timing scale may be adjusted by varying the speed of the sawtooth timing signal. If desired, any portion of the timing sweep may be expanded in accordance with established oscillographic technique.

lFigure 3 is a diagram indicating a plurality of ionized particle paths 43 from the ion source 9 after acceleration in the ion accelerating space between the ion source 9 and the accelerating electrode I'I in a modification of the .device of Fig. 1. The accelerated ions pass through a plurality of .apertures I9, traverse the separating space 2| and impinge upon the signal plate target 23.

A much more eicien-t type of system for a device similar to Fig. 1 but having a relatively large ion source area is shown in Figure 4 wherein the ion source 9- and accelerating electrode I'I are curved to focus the accelerated ions at a common point 45 on the signal plate target 2,3. The focused ion beam arrangement of Fig. 4, in combination with a positive lbias 4l applied to the accelerating space during the time intervals between the occurrence of negative accelerating pulses 35, permits higher gas pressures to be employed (providing substantially all of the gas is completely ionized) thereby increasing the lsensitivity of the system and providing greater signal output from the target electrode 23.

In a tube operated by short duration accelerating pulses 35, a steady deflecting field can be applied to part or all of the separating space, or to both the accelerating and separatingspaces. The particles of different mass may be caused to strike different parts of the target electrode 23, or ionized particles of predetermined mass may be deiiected to a collector electrode 49 as shown in Figure 5. vIf a short duration decelerating pulse is applied to a pair of decelerating electrodes 53 disposed in the path of the ionized beam 43, preferably in the separating space 2|, and the decelerating pulse is applied at the proper time, it will decelerate only those particles of a desired atomic weight whereby a deflecting field provided by deflecting electrodes 55 will deflect particles of said predetermined atomic weight to the collector electrode 49 without substantially deflecting or affecting the velocity of particles of other atomic weights.

Figure 6 shows a second embodiment of the invention wherein the ionized particles traversing the separating space 2l after acceleration by the accelerating electrodeV i1 are caused to travel divergent paths by means of an electromagnetic field applied thereto from an external source, not shown. The ions traversing the divergent paths 43 impinge upon an ion-sensitive mosaic 51 to develop thereon potentials corresponding to the velocities and quantities of such ions. The mosaic 51 is scanned by an electron beam 59 produced by an electron gun, electron focusing elements and electron beam deflection elements.

The apparatus comprising the electron beam generating and deflection means may comprise a thermionic cathode 6I, an anode 63, biased positively with respect to the cathode, an electron lens electrode 65, and a pair of electron beam deflecting elements 61, 59. Deflection voltages applied to the deflection electrodes 51, 69 cause the electron beam 59 to traverse the mosaic 51, (in the same manner as in television iconoscope pickup tubes), thus changing the cathode potential with respect to the mosaic potential and providing, from the cathode, output voltages characteristic of the relative abundance and travel times of the ions impinging on the mosaic,

The output voltage derived from the cathode 6I may be applied to the vertical deilecting elements of a cathode ray oscilloscope in the same manner as described heretofore by reference to the circuit of Fig. l. The accelerating pulses applied to the :accelerating electrode I1 and the deflection voltages applied to the deflection electrodes 61, 59 may be synchronized with the timing generator of the indicating oscilloscope in the same manner as described in the circuit of Fig. l.

Each of the embodiments of the invention described heretofore may be operated according to the following methods of pulsing, accelerating, decelerating and deiiecting the ion beam. In Figure 7, a short duration, negative pulse is applied to the accelerating electrode I1 which establishes a short duration eld in the accelerating space. The accelerated ion beam passing through the aperture I9 in the accelerating electrode I1 traverses the separating space 2| and impinges upon a signal plate target 23. Since the accelerating pulse is completed before the lightest ions leave the accelerating space, all of the ions are accelerated as a direct function of their respective atomic weights. Ions of each atomic weight are hunched together in passing through the separating space and impinge upon the target 23 at successive time intervals. The voltage pulses established upon the target electrode 23 are amplified by the amplifier 25 and are applied to the vertical deecting elements of the oscillograph 29. If a linear timing voltage, such as a voltage of sawtooth waveform, 'is applied to the horizontal deiiecting elements of the oscilloscope, the vertical pips will vhave magnitudes corresponding rto the relative abundance of the ions of the several atomic weights, and the vhorizontal vspacing of the pips will be linearly characteristic of the respective 'atomic weights. v Y

Figure 8 illustnates a system of the general typeV described heretofore wherein a relatively long duration'v accelerating pulse 35 is applied t0 the accelerating space. The accelerating pulse is of sufficient duration so that the ionized particles of interest have left the accelerating space before the completion of the accelerating pulse. With this arrangement the travel times of the. ions of theseveral atomic weights of interestfwill be proportional to the square roo'tofA the mass of the particles, and the heavier particlesv may provide indications on thecathode'ray oscilloscope which overlap on the higher atomic weight end of the oscilloscope horizontal scale.

-If a differentiating and clipper circuit is serially interposed between the amplifier 25 and the vertical deflecti'ng elements of the oscilloscope 29, sharp separated vertical pips Vmay be obtained throughout the length of the Voscilloscope timing scale. By differentiating the amplified pulses derived from the target 23, short duration pulses of opposite polarity will be obtained from each pulse established upon the target electrode. Only a predetermined positive or lnegative portion of the differentiated pulse pairs is selected and applied to the oscilloscope vertical deflecting elements, and the remainder of the differentiated pulses are rejected. Such differentiating and clipper circuits are well known in the electrical wave shaping arts.

The indications provided upon the oscilloscope screen will be as shown in graph 11 wherein the pips at the right-hand side of the timing scale, and corresponding to particles of relatively high atomic weight, are more closely spaced than at the left-hand side of the scale where the pips correspond to particles of relatively lower atomic Weight. f f

If greater separation is desired between the voltage pulses established at the target 23, a positive decelerating pulse 19 may be applied to a decelerating electrode 8|, or to the target 23, to slow down the previously accelerated ions at a time just before the lightest particle to be observed reaches the target electrode. If a relatively short accelerating pulse 35 is applied to the accelerating space, the differentiator and clipper 15 may be omitted, whereas if la relatively longer accelerating pulse is employed, the differentiator and clipper should be included in the circuit, as in the system of Figure 8. The in-` dication provided upon the oscilloscope screen is illustrated in graph 83 wherein the lighter atomic weight indications are crowded rather closely together, and indications of ions exceeding some predetermined atomic weightl are more widely spaced due to the action of the decelerating eld applied to the separating space 2|.

Alternatively, both a short duration accelerating pulse 35 and a short duration decelerating pulse 19, of opposite polarity and immediately following the accelerating pulse, may be applied to the accelerating velectrode |1'in a manner whereby the decelerating pulse 19 is completed before the lightest particle to be examined leaves the accelerating space. This type of operation provides a separation of the indicated pulses equivalent to that obtainable by using a. very much shorter accelerating pulse in the accelerating space for particles ywhich are heavier than some predetermined minimum value,which value may be as low as one.

Figure 11 illustrates the manner in which a negative polarity accelerating pulse 35 is applied to the accelerating electrode Il, and a positive bias 85 is applied to the accelerating electrode during the intervals between successive negative polarity accelerating pulses. The resultant decelerating field applied to the accelerating space tends to keep the ionized particles in the vicinity of the source except during the accelerating pulseintervals. Such operation permits higher gas pressures to be employed (providing the gas is substantially completely ionized), and permits the use of a, much larger area ion source as in the systems of Figs. 3 and 4. A relatively large ion source permits greater signal output to be obtained from the target electrode 23, thereby requiring less amplication. The decelerating bias applied to the yaccelerating space also tends to increase the separation of the indicated pulses on the oscilloscope, since the heavier ion particles are slowed down more than the lighter ones. All ion particles heavier than a predetermined mass, determined by the size and duration of the accelerating pulse, the amount of the' decelerating bias, and the length of the acv celerating space, are decelerated to zero velocity, or less, and returned to the ion source.

Another method of operating the system utilizes either a short durationy or relatively long duration accelerating pulse 35 in the accelerating space, and a positive decelerating bias applied to a decelerating electrode 8| or to the target 83 in the separating space 2l. The decelerating bias should comprise relatively long -pulses 81 occurring between the short duration recurrent accelerating pulses applied to the accelerating space. If a short duration accelerating pulse 3'5 is employed, the diierentiator and clipperl l may be omitted.

The sensitivity of the systems described may be increased, and a more compact unit may be employed, ii' the target 23, or a portion thereof, includes an ion multiplierll. An ion multiplier may be constructed similarly to an 'electron multiplier but the materials employed for secondary ion emission, or for secondary electron emission in response to ion bombardment, are such that the ion beam 43 traversing the separation space 2l initiates operation of the multiplier. It should be understood that the impingi'ngv primary particles on the multiplier are not electrons, but ions having the charge of an electron.

Figure 14 shows a system wherein a -short du-A ration negative polarity, accelerating pulse 35.y

erence to Figure 14, the fluorescent screen also is an ion-responsive signal plate, the abundance of the ions of each observed atomic Weight may be indicated by the relative vertical deflection of `a plurality of pips, as described heretofore by reference to thev system of Fig. 7. At the same time the relative deflection of theions impinging upon the uorescent screen target Will indicate the respective' atomic Weights. The systems of Figs. 14 and 15 merely require that a steady unidirectional deilectingvoltage be applied to the deflecting electrodes 9|, 93 inthe path of the accelerated ion beam 43.

Figure 16 illustrates a system similar to those described by reference to Figs. 14 and 15 Wherein a signal plate 95, or an ion collector, ion mulvtiplier, or combination thereof, of relatively :,l front of the uorescent screen may be adjusted by magneticmeans, such as a solenoid 91 disposed 'outside of the evacuable envelope. V

If desired, the system of Figure 16 may be modified, as shown in Figure 17, so that an adjustable magnetic eld is applied to the device to deflect the ion stream '43 With respect to the target 23 and signal plate 95, so that ions of diierent atomic Weight may be successively analyzed by a iixed signal plate. The magnetic eld is provided by an externally disposed deflection Winding 99 having its axisnormal to the axis of the device. By varying the current through the Winding 99, the Whole ion spectrum may be shifted transverselywith respect to the small signal plate target 95 so that only ions of a desired atomic- Weight impinge upon the signal plate. The magnetic field may be pulsed or varied in any desired manner `for special purposesand for providing special indications.

is applied to the accelerating `electrode l1, and a steady deflecting eld is applied to part or all of the separatingspace, or to the Whole tube. Due to the different'velocities of the ions of different mass, the steady'deecting field will cause the vions to impinge upondiierent parts ofthe target 23. If th'e target is -a fluorescent screen,

so that the points of impingement thereon of the' If Va, relatively long accelerating pulse is appliedy to Athe accelerating electrode l1, a'xed axial magnetic focusing field applied to the separatingY space tends to spread vor separate the paths 'of the ions of different-mass, and an adjustable electrostatic deflection field lapplied transversely to the Iseparating space tends to center the ion spectrum at the image screen.

It should b'e'understood that in each of the deception that a relatively long accelerating pulse 35 is applied to the accelerating' electrode I1, a constant axial magnetic focusing field is estabg lished in the separating space by van external Winding 99 and a variable deflecting electrostaticl field is established between the electrodes 9i. and 93 to deilect the ions of different atomic weight with respect to the fluorescent screen 23 and the target electrode 95. The constant axial magneticffocusing'-iield established by the Windingv provides divergent paths for the ions of different atomic weight, thereby providing a plurality'ofr illuminated spots upon the, fluorescent screen 23. It should be understood that theA target electrode may be a signal plate, an ion It should be understood that the voltages established upon the target electrode 23 may be utilized in any of the Ways `described heretofore,

' for example as in Fig. 7, and that the target 95 may be employed for separate use or measurement of ions of only one predetermined atomic Weight. If separate measurements are desired for ions of a different atomic weight, the relative phasing of the accelerating and deflecting pulses and lill `may be variedV to selections passing `through the deflecting field at earlier or later rrelative times.

In the system of Figure 20, the ion deiiecting plates 9i, 93 extend substantially throughout the length of the separating vspace 2 I. A decelerating pulse 10|, .of relatively short duration and synchronized with the accelerating pulse S5, is applied between the target and accelerating electrodes 23 and of such magnitude and duration as 'to stop completelyV all ions in the separating space 2|.. A unidirectional voltage applied to the defiecting plates 9| and 53 then deflects the ions to the side of the tube, from their positions at the instant of the decelerating pulse. The several diierently deiiected ion beams |03, |05, |91, |09 impinge upon a fluorescent screen disposed parallel to and adjacent with the deflecting plate 93, rwhereby visual indications of the relative atomic weightsV of the deected ions may be obtained in much the same `manner as described Vheretofore by reference Yto the systemv of Figs. `14 and 15. In addition a separate target electrode 23 may be employed, Aif desired, to analyze ions within other mass ranges which are not deected to the fluorescent screen The system of Fig'. 21 is similar in all respects to the system of Fig. Y14 with the exception that a relatively short duration deection pulsev |'UI is applied to the electrostatic deiiection electrodes 91, 93 to provide different deflections 0I accelerated ions within a predetermined velocity range for observation or measurement in re-v sponse to ion impingement on the target electrode 23.- It should be emphasised that lthe deection system of Fig. 14 utilizing a constant dee ection voltage provides deflection of all of the ions in the-separating space, while the system of Figure 21 is vemployed. for providing selective deiiection'only of ions within a predetermined mass range. p

Thus. the invention disclosed herein comprises a. plurality of mass spectrometers for analyzing the composition of gaseous specimens wherein the gas is ionized, the ions are accelerated by square wave,shor t duration, acceleration pulses, and the accelerated ions are continuously indicated as a function of the relative abundance of said ions and the relative travel times of the ions through a fixed separating space. Direct measurements are obtained of the relative abundance Y Y 12 and atomic weights or the ions under tion.

I claim as my invention:

vobserval. A mass spectrometer including, in combination, an envelope containing a source of ions of a material to be analyzed, means for intermittently and successively accelerating and decelerating said ions as a function of their respective atomic weights, Ymeans for .collecting atleast some of said decelerated ions at successiveV time intervals determined by `their relative accelerations, and means for indicating the relative abundance and travel times of said collected ions.

2. A mass spectrometer including, in combina- K tion,'a source of ions of a material to be analyzed, an electrode spaced from said source forming therebetween an ion Vaccelerating space, a source of short duration intermittently recurring ,voltage pulses, means for "applying said pulses to said electrode for intermittently and recurrently accelerating said ions vas a function of their respective atomic Weights, means spaced from said source and accelerating electrodeV for collecting at least some of said ions, a ldecelerating electrode intermediate saidV collecting Vmeans and' said acceleratingspace for decelerating at least some of the ions accelerated through said :accelerating space, means for collecting at least some of said decelerated ions at Asuccessive time intervals determined by their relative .accelerations and means for indicating the relative abundance and travel times of Vsaid ions.

S. A mass spectrometer according vto claim 2 wherein a predetermined Yportion of said accelerated ions are decelerated for a relatively longer time interval than the accelerating .interval or any of said successive 'time intervals.

4. A mass spectrometer including, irl combination, an envelope containing a source of ions of a material'to be analyzed, means for intermittently and recurrently accelerating said `ions as a function of their `respective'atomic Weights, means for decelerating a portion of said accelerated ions, means vfor .collecting at 4leastfsorne of said decelerated ions at successive time intervals determined by their relative accelerations,

means `responsive to ions collected by said col-J' lecting means for generating voltages characteristic of the quantities of said collected ions, 'an oscilloscope, and means for applying said generated voltages to said oscilloscope for indicating the relative travel times ofv said collected ions to indicate the atomic Weights of said collected' ions. *5. A mass spectrometer according to claim 4 wherein said ions are accelerated for intervals Number Name Date 2,331,189 Hipple Oct. 5, 1943 2,344,042 Kali-mann et al. Mar.. 14, 1944 2,387,550

Winkler Oct. 23, 17945 OTHER REFERENCES Atomic Vltnergy for Military Purposes-Report by Henry D. Smyth, Princeton University Press 1945, pages 197 and 198. Copy in Div. 54. 

